The Earth is Flat, there is no curvature , even if it were 50miles away you would not see a curvature because it doesn't exist on a flat plain.
Another favorite “proof” of ball-Earthers is the appearance from an observer on shore of ships’ hulls being obfuscated by the water and disappearing from view when sailing away towards the horizon. Their claim is that ships’ hulls disappear before their mast-heads because the ship is beginning its declination around the convex curvature of the ball-Earth.
Once again, however, their hasty conclusion is drawn from a faulty premise, namely that only on a ball-Earth could this phenomenon occur. The fact of the matter is that the Law of Perspective on plane surfaces dictates and necessitates the exact same occurrence. For example a girl wearing a dress walking away towards the horizon will appear to sink into the Earth the farther away she walks. Her feet will disappear from view first and the distance between the ground and the bottom of her dress will gradually diminish until after about half a mile it seems like her dress is touching the ground as she walks on invisible legs. Such is the case on plane surfaces, the lowest parts of objects receding from a given point of observation necessarily disappear before the highest.